The present embodiments are directed to a lithium-air battery having high capacity and recycle efficiency.
Lithium ion technology has dominated the market as energy source for small electronic devices and even hybrid electric vehicles. However, Li-ion batteries have insufficient theoretical capacity to be a power source for future high capacity generations of power sources capable to run an electric vehicle.
Metal-air batteries have been under investigation as an advanced generation of high capacity energy sources that have the potential to power vehicular devices for distances comparable to present hydrocarbon based combustion engines. In a metal-air battery, the metal of the anode is oxidized and the resulting cation travels to the cathode zone containing a porous matrix of a material such as carbon, for example, where oxygen is reduced and the reduction product as oxide or peroxide combines with the metal cation to form the discharge product. Upon charge, this process is ideally reversed. Metal-air batteries are recognized to have potential advantageous properties over metal ion batteries because the cathodic material, oxygen, may be obtained from the environmental air atmosphere and the capacity of the battery would in theory be limited by the anodic metal supply. Thus, oxygen gas would be supplied continuously from outside the battery and battery capacity and voltage would be dependent upon the oxygen reducing properties and chemical nature of the discharge product formed.
Lithium air batteries have the potential to supply 5-10 times greater energy density than conventional lithium ion batteries and have attracted much interest and development attention as a post lithium ion battery technology. For example, a nonaqueous lithium air battery which forms Li2O2 as discharge product theoretically would provide 3038 Wh/kg in comparison to 600 Wh/kg for a lithium ion battery having a cathodic product of Li0.5CoO2. However, in practice, the metal air technology and specifically current nonaqueous lithium air batteries suffer many technical problems which have prevented achievement of the theoretical capacity.
The capacity of the Li air battery is highly dependent upon the capacity of the cathode matrix to store the Li2O2 discharge product. Li2O2 is generally insoluble in conventional nonaqueous solvents employed in metal air batteries. Therefore, upon formation at the cathode matrix the Li2O2 precipitates and fills the surface porosity of the cathode matrix effectively preventing access to the vacant capacity of the matrix interior region. Moreover, Li2O2 is an insulator and once the surface of the matrix is coated, oxygen reduction is prevented and discharge terminated, i.e., the capacity of the battery is severely reduced in comparison to the theoretical capacity.
One method conventionally employed to increase the capacity of a lithium-air battery is to use an electron conducting support with high surface area such as carbon black as a cathode material. However, even though the surface area is increased, the cathode surface becomes covered by accumulation of the insulative Li2O2 product, resulting in the end of the discharge reaction. Thus, this is not the ultimate solution to improve the capacity.
In U.S. application Ser. No. 14/337,432, filed Jul. 22, 2015, the Applicants described a different solution to the problem to increase capacity by separating the battery into an anode compartment and a cathode compartment separated by a lithium ion conductive ceramic membrane and spatially arranging the air cathode at a minimum distance from the ceramic membrane to reduce lithium ion concentration at the surface of the cathode.
In spite of the significant ongoing effort described above and in the technical community, there remains a need to develop and produce an efficient, safe, cost effective, high capacity lithium air battery useful especially for powering vehicles to distances at least equal to or competitive with current hydrocarbon fuel systems.